The wireless transmission of energy is attractive for many applications in the field of electronics. Energy is transmitted from a transmitter to a receiver based on an inductive, capacitive, or electromagnetic principle. In this way, electrical components or electrical circuits can be supplied with an energy needed for operation if cables and electrical contacts cannot be used.
The most common principle is inductive energy transmission. Typical applications are, for example, chargers for cellular phones, cameras, and electric toothbrushes. This form of wireless energy transmission is also used, however, for electric vehicles and in medical technology for implants or sensors. In principle, the inductive transmission is suitable primarily for applications that allow a small distance between the transmitter and the receiver and have low energy consumption.
For the inductive energy transmission principle, similar to the working principle of a transformer, a variable electromagnetic field is generated in a transmitter coil carrying an alternating current. Due to the variable electromagnetic field received by a receiver coil of the receiver, a voltage is induced in the receiver coil. Due to the load connected to the receiver coil, a current flow is generated by the induced voltage and power is transmitted.
From practice, numerous methods and various applications of wireless energy transmission are known.
U.S. 2014/035383 A1 shows a dual mode receiver for the wireless reception of energy. The receiver comprises an electromagnetic resonator and a receiver coil. A matching network is made up of passive components. The action radius of the electromagnetic resonator includes a first selective low frequency range and a second selective high frequency range, so that an active circuit can be operated in both frequency ranges.
U.S. 2006/0199620 A1 shows a method, a device, and a system for energy transmission. The device comprises a plurality of transmitters that transmit pulse-like energy to a receiver in order to power a load. Here, the receiver needs no DC-DC converter. The transmitter comprises an antenna that communicates with a pulse generator. The pulse generator transmits the pulses of the transmitter. The transmitted current pulses are used only for energy transmission and not for data transmission.
In applications for determining a physical measuring variable by sensors, the wireless transmission of data is a frequently used alternative to often expensive structures with a cable.
DE 100 19 539 A1 shows a sensor with wireless energy supply and a method for wireless energy transmission. A sensor unit has an oscillating circuit consisting of a capacitor and a coil for measurements, for the reception of electromagnetic waves, and for the formation of a sensor signal. By the use of a converter or a filter, a separation of the sensor signal into a feed component and a usable signal component is achieved. The sensor is supplied with energy electrically during the measuring process.
In DE 10 2006 015 111 A1, a rotating bearing is shown with two bearings parts that move opposite each other and between which there is lubricating grease. The lubricant properties are monitored by a lubricant sensor that has at least one piezoelectric element. The lubricant sensor is connected to an evaluation device by signal transmission paths. The signal transmission can take place over wires or a wireless transmission path. The sensors should be supplied with energy from an evaluation device, but it is not specified how this can take place for wireless signal transmission.
U.S. 2002/050754 A1 shows a bearing with a non-contact signal transmission mechanism. A ring magnet is mounted on an outer ring of the bearing by a magnet retaining unit. A coil retaining unit with a generator coil is arranged on an inner ring and turned toward the ring magnet. A structural unit with a transmission circuit and a loop antenna is connected to the coil retaining unit. The rotation of the inner ring causes the generator to produce current. The generated energy is fed to a transmission circuit. An output signal of a sensor is transmitted through the transmission circuit as a low-energy wave via the loop antenna and received by a stationary side.
DE 10 2012 015 000 A1 shows an electric installation device with a charging station for mobile devices. A charging shell comprises a primary charging coil that is connected to a power source with a processing and control unit. A secondary charging coil of the mobile device is provided with energy through inductive energy transmission.
Due to more and more mobile devices that are powered by rechargeable energy sources, there is a plurality of charging devices for wireless energy transmission with different technical features. The consumer is uncomfortably confronted with this plurality of devices that also require different cables. As a reaction to the need for simplification and standards, a collection of companies, the Wireless Power Consortium, has been formed and has developed the so-called Qi standard for interoperability of devices, especially charging devices. The details of this standard are available, for example, at: http://www.wirelesspowerconsortium.com/developers/specification.html
Qi technology allows the wireless inductive transmission of energy in a low-power range of up to 5 W in a transmission frequency range from 110 Hz to 205 Hz and at an operating voltage of the transmitter of 19 V. The transmitter-receiver coils have a planar design and are typically arranged at a distance of 5 mm opposite each other. The basic configuration for Qi technology provides a base station with a transmission coil that transmits energy to a receiver unit with a receiver coil. Here, the receiver unit is regularly coupled with an accumulator to charge it electrically. The receiver unit also communicates unidirectionally with the transmitter unit over allocated monitoring units to be able to perform specific power matching through load modulation.
EP 2 709 231 A1 shows an energy supply system for a field device connected to a wired network. The energy supply system is equipped with a radio module for data communications with an external unit. The radio module is connected to the field device and has a power supply. A power supply adapter comprises an energy transmitter for wireless energy transmission. A power supply unit comprises an energy receiver that is coupled inductively with the energy transmitter. Energy transmitters and energy receivers correspond to the Qi standard.
WO 2014/020464 A2 shows an operating method for an inductive energy transmission from a transmitter to a receiver by means of a power signal, wherein the energy transmission system is compatible with the Qi standard. The energy transmission system provides expanding the unidirectional communication of the receiver with the transmitter corresponding to the Qi standard and enabling communications, starting from the transmitter, between the transmitter and receiver. Here, the communications are based on a load modulation of the power signal.